The present invention relates to a wire guide or stylet assembly for the introduction of pacing or defibrillation leads and medical catheters to a desired site within a patient""s body. Specifically, this invention relates to a steerable stylet assembly that imparts a desired dynamic curvature in the distal portion of a catheter or lead during its introduction. Such curvature is required to guide the catheter or lead through the patient""s vascular system to a desired site within the heart. The present invention uses braided flat wire wrapped around a tubular member that allows the physician user to apply, via a handle equipped with a rotatable knob, enhanced torsional transfer strength to the stylet, making it easier to effect and maintain the desired curvature to the lead or catheter.
Generally speaking, pacing and defibrillation leads and catheters are highly flexible throughout their length so as to flex with the movement or contraction of the heart as well as other body or muscular movement. Such flexibility avoids the fracture of the lead body due to cumulative stress over time. As a result, however, implantable pacing and defibrillation leads and catheters are often too limp to be advanced through the venous system to a desired internal site within the patient""s cardiovascular system. To assist in the placement of such devices, a thin stiffening stylet is inserted into the lumen of a lead or a steerable catheter to guide its passage through the venous system and ensure its proper placement at a desired site within the patient""s heart or into a vessel, such as the coronary sinus. This thin wire stylet is inserted into the proximal opening of a lumen found in the lead connector pin, or in an accessory (secondary) lumen in the catheter, and extends down the length of the device. The stylet stiffens the entire assembly and may be bent at the distal end by a physician prior to placement within the lumen to provide a bend or curvature to the lead or catheter. The curved distal portion facilitates movement of the distal lead tip through the venous system and to the desired site within the patient""s heart or other vessel within the cardiovascular system.
Many different types of stylets are available to aid in steering a catheter or lead. For example, some stylets must be provided with a desired shape prior to insertion of the stylet within the lead or catheter. From time to time, as a physician directs the distal tip of the lead or catheter to a desired location, it may be necessary to withdraw the stylet and insert a new stylet with a different curvature. This process of substituting a new and differently curved stylet may be used whenever a new obstacle to lead advancement is encountered.
This technique, however, has several drawbacks. For example, repeated insertion and withdrawal of the stylet may contaminate the lead lumen with blood. This is undesirable because drying blood may clot and jam the stylet within the lead, making stylet removal difficult and, perhaps, impossible, and thereby rendering the lead unusable. Moreover, the continued insertion, withdrawal, and substitution of other stylets is time consuming and has the potential for damaging the lead, the blood vessel, or both.
In order to avoid repeated withdrawal and reintroduction of stylets, other types of stylets have been proposed including those in U.S. Pat. No. 4,381,013 issued to Dutcher and U.S. Pat. No. 4,677,990 issued to Neubauer, both incorporated herein by reference in their entireties. A further example of a steerable stylet is disclosed in U.S. Pat. No. 4,846,175 assigned to Frimberger.
More recently, two alternative mechanisms have been proposed to make steerable stylets more useful. The first mechanism was proposed in U.S. Pat. No. 5,396,902 issued to Brennan, incorporated herein by reference in its entirety. The ""902 patent discloses the use of a steerable stylet which can be deflected and curved within the lead during placement within the body via a manipulative handle coupled to the proximal end of a slotted, tubular member located at the distal end of the stylet via a pull (or tension) wire. Tension applied to the pull wire causes the distal end of the stylet to be deflected and curved to match the requirements of the physician during lead placement. The second mechanism appears in U.S. Pat. No. 6,027,462 issued to Greene, incorporated herein by reference in its entirety. The ""462 patent discloses a handle which uses a rotating knob to effect the deflection of the tubular member, thereby providing curvature to the stylet and endocardial lead assembly.
The foregoing examples of stylet embodiments discuss the various mechanisms utilized to facilitate deflection of the distal end. To further facilitate tip deflection, material selection is important. In one embodiment, a stylet may be manufactured from a material having a very large elasticity. For example, a superelastic nickel-titanium alloy (nitinol) could be used for this purpose. By employing a material that is highly elastic, a large bending deflection may be sustained by the stylet tip without the tip breaking.
As discussed above, stylet tip deflection provides one mechanism of steering a lead or catheter through the vasculature during placement. Another mechanism involves the rotation of the distal end of the stylet. Once a curvature is introduced into the lead or catheter tip via the deflected stylet, it is often necessary to rotate the curved tip as it is guided into position. Optimally, rotation of the proximal end of a stylet by a predetermined amount will result in rotation of the distal end of the stylet by an equal amount. Although desirable, such one-to-one angular displacement throughout the length of a stylet is not achievable. All materials used to manufacture stylets and guidewires experience some twisting when a torque is applied to one end. This is particularly true of highly elastic metals such as superelastic nitinol generally desirable for use in achieving large stylet tip deflection. This is also particularly true of an elongated body having a small diameter such as a stylet or guidewire, since the torsional strength of a cylindrical body is proportional to the stylet or guidewire diameter to the third power. Thus, although the use of nitinol and other materials such as stainless steel results in a stylet with a highly-deflectable tip, this use has undesirable consequences such as providing a device that is relatively incapable of transferring rotational or angular displacement down the length of the stylet. The problem is exasperated by ever-smaller stylet and guidewire dimensions, as has been the recent trend. What is needed, therefore, is an improved system for transferring rotational force throughout the length of a stylet or guidewire, and for further improving the steerability of a lead or catheter body.
The present invention is directed to an improved version of a steerable guidewire or stylet that includes a braided structure that provides increased torsional strength to the stylet. The invention may be practiced with any type of stylet. In one embodiment, the stylet comprises an elongated tubular member having a pull wire residing within the tubular member. The distal end of the pull wire is anchored to the distal end of the tubular member. One or more apertures may be provided near the distal end of the tubular member located substantially within an elongated region lying parallel to the axis of the tubular member. These one or more apertures provide a preferential bending direction to the tubular member when tension is applied at a proximal end of the pull wire. In one embodiment, these one or more apertures comprise an elongated slot. The deflection capability of the stylet is enhanced by forming the tubular member from nitinol or another highly elastic metal.
As noted above, a braided structure holds the pull wire within the slotted tubular member. This braid may be formed of a metal such as stainless steel flat wire that optionally may be reinforced with polyimide. The braid may be provided along the entire length of the guidewire or stylet, or optionally may be utilized only at the distal tip. This braid greatly improves the torsional strength of the stylet so that rotational force applied at the proximal guidewire end may be transferred to the distal end. This increase in torsional strength is provided without any substantial decrease in the deflection capability of the distal tip of the stylet.
In one embodiment, the stylet or guidewire of the current invention utilizes a handle similar to that disclosed in the ""462 patent. This handle is equipped with a rotatable knob and inner slider member. This knob and slider member may be slid distally relative to the handle to provide a mechanism for quickly forming a curve in the stylet or guidewire. This feature is particularly beneficial when a curve is needed only temporarily, for example in conjunction with deflecting the tip of the stylet, to facilitate entry into a desired blood vessel, such as the coronary sinus. Alternatively, the knob may be rotated to provide a larger deflection at the distal stylet tip. This handle provides a deflection mechanism having a minimum number of moving parts, and which is arranged to facilitate easy control of the degree of curvature displayed by the stylet or guidewire using only one hand.
Another embodiment of a handle that may be used with the current invention is shown and described in the Application Ser. No. 09/659,797 entitled xe2x80x9cMethod and Apparatus for Deflecting a Screw-In Leadxe2x80x9d, filed on even date herewith, and which is incorporated by reference in its entirety. This handle structure includes a detachable lead extension tool for coupling to a lead body, particularly for extendable-retractable leads. The disclosed system adapts the length of the lead to match a stylet, and further facilitating the ease with which deflection of a stylet tip may be accomplished.